1. Field of the Invention
The present invention relates to a high-frequency circuit in which a high-frequency filter is parallel installed to an integrated circuit.
2. Description of the Related Art
Conventionally, a television tuner that has a mixer for converting an UHF band television signal or a VHF band television signal into an intermediate band television signal by converting the frequency of the UHF or VHF band television signal, an intermediate frequency band amplifier for amplifying the intermediate frequency band television signal, and a SAW filter, which includes a trap circuit for attenuating video and audio intermediate frequency signals of a channel adjacent to the intermediate frequency band, interposed between the mixer and the intermediate frequency amplifier has been proposed (for example, see JP-A-H11-69245 or JP-A-2003-318754).
FIG. 2 is a diagram illustrating the configuration of a television tuner described in JP-A-11-69245. A television signal of a specific channel in the UHF or VHF band selected by a tuning circuit or the like, which is not shown in the figure, is input to a mixer 101 through an input terminal 101a, and a local oscillator signal is input to the mixer 101 from a local oscillator 102. In the mixer 101, the input UHF or VHF band television signal is mixed with the local oscillator signal, and thereby being converted into an intermediate frequency band television signal. Here, the intermediate frequency band television signal will be abbreviated as an intermediate frequency signal. The intermediate frequency signal output from the mixer 101 is input to an intermediate frequency amplifier 104 through a SAW (surface acoustic wave) filter 103 that is an intermediate frequency band pass filter. The intermediate frequency signal input to the intermediate frequency amplifier 104 is amplified and is detected by a video detector 105 having a synchronization detecting circuit, and a video signal V is output from the video detector 105.
As shown in FIG. 3, the mixer 101, the intermediate frequency amplifier 104, and the video detector 105 are configured as one integrated circuit 108. In this integrated circuit 108, output terminals 101b and 101c of the mixer 101 and input terminals 104a and 104b of the intermediate frequency amplifier 104 are disposed. Input terminals 103a and 103b of the SAW filter 103 are connected to the output terminals 101b and 101c of the mixer 101 through a capacitor 106. In addition, output terminals 103c and 103d of the SAW filter 103 are connected to the input terminals 104a and 104b of the intermediate frequency amplifier 104 through a capacitor 107.
By using the above-described configuration, the SAW filter 103 is connectable in a simple manner and the intermediate frequency amplifier 104 and the video detector 105 can be directly connected together, and thereby the configuration of the integrated circuit 108 becomes simple.
However, in the conventional television tuner, since the output terminals 101b and 101c of the SAW filter 103 and the input terminals 104a and 104b thereof are disposed to be adjacent to each other on one side of the integrated circuit 108, the input and output sides of the SAW filter 103 are capacitively coupled, and thereby there is a problem that the original characteristics of the SAW filter 103 cannot be acquired.
In addition, since terminal pitches (for example 1.78 mm to 2.5 mm) of the SAW filter 103 are much larger than terminal pitches (for example, 0.5 mm to 0.65 mm) of the output terminals 101b and 101c and the input terminals 104a and 104b which are disposed on one side of the integrated circuit 108, there is a problem that it is difficult to effectively use a mounting space for disposition of the SAW filter 103 and the peripheral components.